In an advanced aircraft being developed for military applications, a gas turbine engine pivotally mounted at the end of each wing of the aircraft drives a corresponding one of a pair propeller-like rotors. The engines have a vertical flight mode wherein the rotors effect vertical takeoffs and landings in helicopter-like fashion. Between takeoffs and landings, the engines have a horizontal flight mode wherein the rotors propel the aircraft in fixed wing fashion for maximum speed and maneuverability.
In commonly owned United U.S. patent application Ser. No. 222,994, filed concurrently with this patent application by Warren N. Holcomb to the assignee of this invention, and now allowed, a secondary oil system particularly suited for such flight propulsion gas turbine engines is described. The aforesaid secondary oil system includes an annular secondary oil tank in an internal sump of the engine from which a gravity induced secondary oil flow is continuously directed to a bearing in the sump. An inlet from the primary oil system of the engine to the secondary tank is at the top of the tank and a discharge from the tank is at the bottom thereof in both the horizontal and vertical flight modes. If primary oil flow stops, gravity induced secondary oil flow persists in both the horizontal and vertical flight modes until the secondary tank completely drains through the discharge. The duration of the secondary oil flow is calculated to permit the aircraft to fly horizontally to a landing area and then to land vertically. A new and improved secondary oil system according to this invention incorporates partitions in the secondary oil tank to assure a minimum secondary oil supply for vertical descent and to improve the gravity induced secondary oil flow.